In general and with reference to FIG. 1 it is recognized that an assembly that requires a bolt thread 1, of standard proportions, to be inserted into a pre-threaded nut 2, of standard proportions, can often result in a condition where the crest of the bolt thread 10, 10a makes initial contact with the root of the nut thread. The counter rotation of the nut and bolt threads may then cause the threads to jam into each other 3, 3a and will further restrict the action of the mating threads from achieving relative axial movement of the nut anchor and the bolt. As is well known to those skilled in the art, this action is termed “cross threading”.
As will be appreciated by those skilled in the art, cross threading becomes more prevalent where the axes of the bolt thread 4 and the nut thread 5 are out of angular alignment at the initial point of assembly. It requires only a small misalignment of axes 4 and 5 to create this adverse assembly condition.
Many attempts have been introduced to bolt lead entry threads and/or nut entry threads, to overcome this adverse assembly condition. Exemplary anti-cross threading devices are described in U.S. Pat. No. 7,334,975, entitled FASTENER ASSEMBLY, by Jungman, et al, U.S. Pat. No. 7,438,512, entitled U-BOLT ASSEMBLY, by Jakuszeski, et al. and U.S. Pat. No. 5,836,731, entitled ANTI-CROSS THREADED FASTENER, by Goodwin et al, the contents of each are hereby incorporated by reference.
An example of the systems in current use can be viewed in relation to FIG. 2. Conventional systems rely upon changes to the bolt lead entry point geometrical configuration 14 that is aimed toward encouraging the lead threads of the bolt to slide over the nut thread root diameter and to assist in the mating threads creating thread pitch engagement and minimize cross threading. The above noted prior art recognizes that the circular (or radius) cross section of the lead entry threads 14 may not achieve this aim and anticipate that an additional plain dog point of circular cross section or of a special form that diminishes in magnitude as the section approaches the bolt entry end may be a requirement toward resisting nut and bolt threads from cross threading.
In each of these cases, the axial pitch 12 of the bolt lead entry threads are maintained at the same numerical value as the standard pitch of the bolt and nut threads. Without the extended point feature and with a small amount of misalignment between the nut and bolt axes, it remains a possibility for the initial assembly conditions as outlined and discussed in relation to FIG. 1 to be present and, due to the influence of the constant thread pitch 12, cross threading will still occur.